A barcode is an optical machine-readable representation of information. Devices for identifying or extracting information from barcodes are generally referred to as barcode readers (or barcode scanners). An image-based barcode reader includes a camera for capturing an image of a barcode to be read. The camera includes a focusing lens that focuses light reflected from a target area onto a photo sensor array. Once an image of a barcode has been captured by the camera, a decoder processes the image and extracts the information contained in the barcode.
A barcode reader may include both a bright field illumination system and a dark field illumination system for illuminating a target area. A bright field illumination system typically includes multiple illumination elements (e.g., light-emitting diodes (LEDs)) with refracting and/or diffusing optics designed to direct illumination towards the target area essentially parallel to the optical axis (i.e., a line originating from the center of the focusing lens and extending outward into the center of the camera's field of view). A bright field illumination system may provide optimal illumination for a “far zone” of the camera's field of view, i.e., an area that is located relatively far away from the reader.
A dark field illumination system typically includes multiple LEDs with optics that project illumination from the sides of the reader towards the optical axis at an angle no more than 45 degrees from the plane that is perpendicular to the optical axis. A dark field illumination system may provide optimal illumination for a “close zone” of the field of view, i.e., an area that is nearly in contact with the reader.